The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
In general, in order to operate a drive motor of a green car such as a hybrid car or an electric car, a power module that appropriately transfers electric current supplied from a high-voltage battery to the drive motor is desired.
Such a power module generates considerable heat due to its fast switching operation. Because this heat generation causes a reduction in efficiency of the power module, a cooler is configured to cool the power module.
In a power module having dual-sided cooling, a board is respectively installed on both surfaces of the semiconductor chip of the power module, i.e., an IGBT or a MOSFET, and coolers are installed at outer sides of the board, thereby simultaneously cooling both sides of the board.
In particular, a 2-in-1 type power module using two semiconductor chips and having dual-sided cooling has a small volume and excellent heat dissipation performance, and thus its application range is expanding.
FIG. 1 shows a conventional 2-in-1 type power module having dual-sided cooling.
As shown in FIG. 1, the conventional power module is configured such that an upper board 10 and a lower board 20 are provided in directions of both sides of a first semiconductor chip 31 and a second semiconductor chip 32, and electrodes such as a first output terminal 11, a second output terminal 12, a third output terminal 23, a positive terminal 22, and a negative terminal 21 that are connected to the semiconductor chips 31 and 32 are provided at the boards 10 and 20. The positive terminal 22 is connected to an anode of a battery (not shown), the negative terminal 21 is connected to a cathode of the battery, and the first, second and third output terminals 11, 12, and 23 are connected to a driving motor (not shown). Spacers 41, 42, 43, and 44 made of a copper material may be provided to connect between the upper board 10 and the lower board 20 and to secure a space for installing wires (not shown).
The electrodes of the upper board 10 and the lower board 20 are respectively provided on insulating layers 14 and 25, and the insulating layers 14 and 25 are made of a ceramic material such as alumina (Al2O3). Further, heat dissipating plates 13 and 24 are provided on outer sides of the insulating layers 14 and 25 to transfer heat to coolers 51 and 52.
Meanwhile, as shown in FIG. 3, heat generated in a semiconductor chip 30 is diffused not only in a lengthwise direction but also in a width direction while being transferred to a copper layer C. Heat is diffused at an angle of about 45° in the copper layer C, which has high thermal conductivity, and is diffused in a vertical direction in an insulating layer I, which has relatively low thermal conductivity.
In order to increase cooling efficiency by increasing a heat dissipation area, it is desired to increase thickness of the copper layer C to form a space where heat is diffused in the width direction. However, in a conventional board composed of copper and ceramic materials, there is a problem in that the copper layer C cannot be formed to a certain thickness or more because of difference in thermal expansion coefficient between copper and ceramic materials. When the copper layer is excessively thick, it is difficult to carry out a process of bonding copper and ceramic layers to each other through a eutectic reaction at a temperature of equal to or greater than 1065° C., and breakage is easily caused due to internal residual stress.
As a solution to this, as shown in FIG. 2, a structure in which a copper-ceramic bonding layer is removed from the board, and insulating layers 96 consisting of silicon nitride (Si3N4) are respectively provided between electrodes 91, 92, 93, and 94 and coolers 51 and 52 has been proposed.
However, we have discovered that since silicon nitride (Si3N4) is relatively expensive and is exposed to the outside of a sealing member 80, it is vulnerable to breakage due to an external impact.
In addition, it is difficult to bond the insulating layers 96 and the electrodes 91, 92, 93, and 94 with a thermal grease 60, and when the thermal grease 60 is not uniformly applied, thermal characteristics are rapidly deteriorated.
The foregoing is intended merely to aid in the understanding of the background of the present disclosure, and is not intended to mean that the present disclosure falls within the purview of the related art that is already known to those skilled in the art.